1. Technical Field
The present invention relates to an air conditioner for cooling and dehumidifying a room to be air-conditioned.
2. Related Art
An air conditioner, having a cooling operation function and a dehumidifying operation function has hitherto adopted a weak-cooling or re-heating dehumidifying operation function. Under weak-cooling humidifying operation, the temperature of a room to be air-conditioned decreases simultaneously with dehumidification. Therefore, this operation has a problem that the dehumidification amount is also reduced with time lapse or user's feeling temperature is reduced, so that users have feeling of discomfort. The re-heating dehumidifying operation temporarily reduces the temperature of air to condense water in the air. The temperature-reduced air is then re-heated and supplied to a room to be air-conditioned. This operation has a problem that either the cooling capacity decreases or energy consumption increases.
Therefore, there has been recently known an air conditioner which adopts a combination of a refrigeration cycle including a compressor, a radiator, an expansion valve and an evaporator and a desiccant rotor as moisture adsorbing means as disclosed in JP-A-2001-241693. According to this type of air conditioner, outdoor air taken into the air conditioner is made to flow through a desiccant so that moisture in the take-in air is adsorbed in a moisture adsorbent area of the desiccant rotor, the thus-dehumidified air is supplied to the evaporator to adsorb heat, and then the air which has been set to proper temperature and humidity as described above is supplied into a room to be air-conditioned. The moisture adsorbed in the desiccant rotor is desorbed from the desiccant rotor by using exhaust heat from the radiator in a regenerating area of the desiccant rotor, thereby regenerating the desiccant rotor.
Air conditioners utilizing desiccant rotors for dehumidification have traditionally been constructed so that air taken into the air conditioner is first dehumidified by the desiccant rotor and then the dehumidified air is made to flow into an evaporator, thus reducing the latent heat load in the evaporator. The dehumidification capacity of the desiccant increase as the relative humidity difference between the moisture-adsorbing area and the regenerating area of the desiccant rotor increases. Therefore, in order to enhance the dehumidification performance of the desiccant rotor, it is required to either increase the temperature of the regenerating area or increase the relative temperature of the regenerating area by the flow of cooling air to the processing side. However, when the air taken into the air conditioner is made to directly flow to the desiccant as a first step in air conditioning, there is a problem that the temperature of the moisture-adsorbing area of the desiccant is risen, and thus the dehumidifying performance of the desiccant is lowered.
Furthermore, in order to enhance the dehumidifying performance of the desiccant, it is required to increase the temperature of the regenerating area, so that the load at the refrigeration cycle side is increased and the efficiency of the refrigeration cycle is lowered.
Furthermore, adsorbents used as desiccant material, such as silica gel, zeolite or the like, adsorb moisture at relatively low humidity. It is necessary to heat these adsorbents up to 80 to 150 deg C. to desorb the moisture. Recently, an air conditioner using a heat pump type refrigeration cycle containing carbon dioxide gas refrigerant, and having a low global warming potential (GWP) has been promoted for development. However, even in a heat pump type refrigeration cycle having large exhaust heat, air is heated to 60 to 80° C. at the highest by heat from a radiator. This temperature range is insufficient for regeneration of the desiccant. Accordingly, as disclosed in JP-A-2005-201624, supplied air is cooled by a low-temperature heat source (evaporator) of the heat pump before moisture in the supplied air is adsorbed by the desiccant rotor, whereby the temperature difference between the adsorbing area and the regenerating area of the desiccant rotor is increased and the dehumidifying performance of the desiccant rotor is enhanced.
However, when the evaporator is placed in the upstream side of the air supply side of the desiccant, the latent heat load in the evaporator cannot be reduced. Furthermore, the temperature of supplied air which has passed through the desiccant is increased by adsorbent heat. Therefore, the load on the refrigeration cycle increases, and in the heat pump type refrigeration cycle, which originally has a low refrigeration cycle efficiency when it is used for cooling, either sufficient cooling capacity cannot be obtained or the temperature of the moisture adsorbing area of the desiccant rotor increases and regeneration of the desiccant rotor is insufficient.